U.S. patent application number 10/601622 was filed with the patent office on 2004-04-08 for fault diagnosis apparatus of fuel evaporation/dissipation prevention system.
Invention is credited to Kanao, Hidetsugu, Saito, Kenji.
Application Number | 20040068360 10/601622 |
Document ID | / |
Family ID | 30447626 |
Filed Date | 2004-04-08 |
United States Patent
Application |
20040068360 |
Kind Code |
A1 |
Saito, Kenji ; et
al. |
April 8, 2004 |
Fault diagnosis apparatus of fuel evaporation/dissipation
prevention system
Abstract
When a first restoring pressure amount, measured after a fault
diagnosis object region is in a reduced pressure state, exceeds a
first or second judgment value, a second restoring pressure amount
is measured by releasing the fault diagnosis object region to the
atmosphere and then sealing it. When the first restoring pressure
amount is between the first and second judgment values, the second
restoring pressure amount is compared with a third judgment value.
When the first restoring pressure amount exceeds the second
judgment value, the second restoring pressure amount is compared
with a fourth judgment value. Leak is determined to exist when the
first restoring pressure amount exceeds the first judgment value
and the second restoring pressure amount does not exceed the third
judgment value, or when the first restoring pressure amount exceeds
the second judgment value and the second restoring pressure amount
does not exceed the fourth judgment value.
Inventors: |
Saito, Kenji; (Nagoya-shi,
JP) ; Kanao, Hidetsugu; (Okazaki-shi, JP) |
Correspondence
Address: |
BIRCH STEWART KOLASCH & BIRCH
PO BOX 747
FALLS CHURCH
VA
22040-0747
US
|
Family ID: |
30447626 |
Appl. No.: |
10/601622 |
Filed: |
June 24, 2003 |
Current U.S.
Class: |
701/114 ;
73/114.39; 73/114.41; 73/114.45 |
Current CPC
Class: |
F02M 25/0809
20130101 |
Class at
Publication: |
701/114 ;
073/118.1 |
International
Class: |
F02D 041/22 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 25, 2002 |
JP |
2002-185129 |
Apr 24, 2003 |
JP |
2003-120518 |
Claims
What is claimed is:
1. A fault diagnosis apparatus of a fuel evaporation/dissipation
prevention system for collecting an evaporated fuel occurring
inside a fuel tank into a canister and introducing the evaporated
fuel into an intake passage of an internal combustion engine,
comprising: first diagnosis means for serially comparing a first
restoring pressure amount measured after a fault diagnosis object
region of said fuel evaporation/dissipation prevention system is
brought into a reduced pressure state, with a first judgment value
and with a second judgment value greater than said first judgment
value; second diagnosis means for measuring a second restoring
pressure amount by sealing said fault diagnosis object region after
an atmospheric pressure is introduced into said fault diagnosis
object region when said first restoring pressure amount measured by
said first diagnosis mean is greater than said first judgment value
or said second judgment value, then comparing said second restoring
pressure amount with a third judgment value when said first
restoring pressure amount is greater than said first judgment value
but is smaller than said second judgment value, and comparing said
second restoring pressure amount with a fourth judgment value
greater than said third judgment value when said first restoring
pressure amount is greater than said second judgment value; and
abnormality judgment means for judging said fuel
evaporation/dissipation prevention system as being abnormal when
said first restoring pressure amount measured by said first
diagnosis means is greater than said first judgment value but is
smaller than said second judgment value and said second restoring
pressure amount measured by said second diagnosis means is smaller
than said third judgment value, or when said first restoring
pressure amount is greater than said second judgment value and said
second restoring pressure amount is smaller than said fourth
judgment value.
2. A fault diagnosis apparatus of a fuel evaporation/dissipation
prevention system for collecting an evaporated fuel occurring
inside a fuel tank into a canister and introducing the evaporated
fuel into an intake passage of an internal combustion engine,
comprising: first diagnosis means for comparing a first restoring
pressure amount measured after a fault diagnosis object region of
said fuel evaporation/dissipation prevention system is brought into
a reduced pressure state, with a first predetermined value; second
diagnosis means for comparing a second restoring pressure amount
measured under a sealed state of said fault diagnosis object region
after an atmospheric pressure is introduced into said fault
diagnosis object region, with a second predetermined value set in
accordance with said first restoring pressure amount when said
first restoring pressure amount measured by said first diagnosis
means is greater than said first predetermined value; and
abnormality judgment means for judging said fuel
evaporation/dissipation prevention system as being abnormal when
said first restoring pressure amount measured by said first
diagnosis means is greater than said first predetermined value and
said second restoring pressure amount measured by said second
diagnosis means is smaller than said second predetermined
value.
3. A fault diagnosis apparatus of a fuel evaporation/dissipation
prevention system according to claim 2, wherein said first
diagnosis means measures said first restoring pressure amount after
a set time passes from completion of pressure reduction of said
fault diagnosis object region, and said second diagnosis means sets
said second predetermined value to a greater value when said first
restoring pressure amount measured by said first diagnosis means is
greater.
4. A fault diagnosis apparatus of a fuel evaporation/dissipation
prevention system for collecting an evaporated fuel occurring
inside a fuel tank into a canister and introducing the evaporated
fuel into an intake passage of an internal combustion engine,
comprising: first diagnosis means for serially comparing a first
restoring pressure amount measured after a fault diagnosis object
region of said fuel evaporation/dissipation prevention system is
brought into a reduced pressure state, with a first judgment value
and a second judgment value greater than said first judgment value;
second diagnosis means for measuring a second restoring pressure
amount by sealing said fault diagnosis object region after an
atmospheric pressure is introduced into said fault diagnosis object
region when said first restoring pressure amount measured by said
first diagnosis mean is greater than said first judgment value or
said second judgment value, then comparing said second restoring
pressure amount with a third judgment value when said first
restoring pressure amount is greater than said first judgment value
but is smaller than said second judgment value, and comparing said
second restoring pressure amount with a fourth judgment value
greater than said third judgment value when said first restoring
pressure amount is greater than said second judgment value;
abnormality judgment means for judging said fuel
evaporation/dissipation prevention system as being abnormal when
said first restoring pressure amount measured by said first
diagnosis means is greater than said first judgment value but is
smaller than said second judgment value and said second restoring
pressure amount measured by said second diagnosis means is smaller
than said third judgment value, or when said first restoring
pressure amount is greater than said second judgment value and said
second restoring pressure amount is smaller than said fourth
judgment value; and correction means for correcting and decreasing
said fourth judgment value to be compared by said second diagnosis
means with said second restoring pressure amount when the
atmospheric pressure changes and decreases while said first
diagnosis means measures said first restoring pressure amount.
5. A fault diagnosis apparatus of a fuel evaporation/dissipation
prevention system according to claim 4, wherein said correction
means corrects and decreases said fourth judgment value in
accordance with the decrement of the atmospheric pressure while
said first diagnosis means measures said first restoring pressure
amount.
6. A fault diagnosis apparatus of a fuel evaporation/dissipation
prevention system according to claim 4, wherein said correction
means replaces said fourth judgment value by said third judgment
value when the atmospheric pressure changes and decreases beyond a
predetermined pressure while said first diagnosis means measures
said first restoring pressure amount.
7. A fault diagnosis apparatus of a fuel evaporation/dissipation
prevention system for collecting an evaporated fuel occurring
inside a fuel tank into a canister and introducing the evaporated
fuel into an intake passage of an internal combustion engine,
comprising: first diagnosis means for serially comparing a first
restoring pressure amount measured after a fault diagnosis object
region of said fuel evaporation/dissipation prevention system is
brought into a reduced pressure state, with a first judgment value
and with a second judgment value greater than said first judgment
value; second diagnosis means for measuring a second restoring
pressure amount by sealing said fault diagnosis object region after
an atmospheric pressure is introduced into said fault diagnosis
object region when said first restoring pressure amount measured by
said first diagnosis mean is greater than said first judgment value
or said second judgment value, then comparing said second restoring
pressure amount with a third judgment value set in accordance with
said first restoring pressure amount when said first restoring
pressure amount is greater than said first judgment value but is
smaller than said second judgment value, and comparing said second
restoring pressure amount with a fourth judgment value set in
accordance with said first restoring pressure amount when said
first restoring pressure amount is greater than said second
judgment value; abnormality judgment means for judging said fuel
evaporation/dissipation prevention system as being abnormal when
said first restoring pressure amount measured by said first
diagnosis means is greater than said first judgment value but is
smaller than said second judgment value and said second restoring
pressure amount measured by said second diagnosis means is smaller
than said third judgment value, or when said first restoring
pressure amount is greater than said second judgment value and said
second restoring pressure amount is smaller than said fourth
judgment value; and correction means for correcting and decreasing
said third judgment value or said fourth judgment value to be
compared by said second diagnosis means with said second restoring
pressure amount when the atmospheric pressure changes and decreases
while said first diagnosis means measures said first restoring
pressure amount.
8. A fault diagnosis apparatus of a fuel evaporation/dissipation
prevention system according to claim 7, wherein said correction
means corrects and decreases said third judgment value or said
fourth judgment value in accordance with the decrement of the
atmospheric pressure during measurement of said first restoring
pressure amount by said first diagnosis means.
Description
[0001] The entire disclosure of Japanese Patent Application No.
P2002-185129 filed on Jun. 25, 2002 and Japanese Patent Application
No. P2003-120518 filed on Apr. 24, 2003 including specification,
claims, drawings, and summary is incorporated herein by reference
in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a fault diagnosis apparatus of a
fuel evaporation/dissipation prevention system.
[0004] 2. Description of the Related Art
[0005] A fuel evaporation/dissipation prevention system is provided
in an automobile to prevent emission of evaporated fuel occurring
inside a fuel tank into the atmosphere. The fuel
evaporation/dissipation prevention system includes a canister, a
vapor passage extending between a fuel tank and the canister and
having a purge valve fitted thereto, and a purge passage extending
between the canister and an intake passage of an internal
combustion engine. The canister adsorbs the evaporated fuel inside
the fuel tank through the vapor passage. On the other hand, the
purge valve is opened under a predetermined condition so that the
evaporated/dissipated fuel adsorbed to the canister can be purged
into the intake passage of the internal combustion engine through
the purge passage.
[0006] A fault diagnosis apparatus for detecting leak abnormality
of the fuel evaporation/dissipation prevention system is provided
to this prevention system. The fault diagnosis apparatus includes a
vent valve fitted to the canister, a pressure sensor for detecting
an internal pressure of the fuel tank, and an electronic control
unit (ECU) for inputting detection information from the pressure
sensor and controlling opening/closing of the vent valve and the
purge valve. To make fault diagnosis, the fault diagnosis apparatus
opens the purge valve and closes the vent valve to bring the fuel
tank, the vapor passage, and the purge passage as the fault
diagnosis object regions of the fuel evaporation/dissipation
prevention system into a predetermined negative pressure state. The
fault diagnosis apparatus then closes the purge valve, measures the
internal pressure of the fuel tank while the fault diagnosis object
regions are thus closed, and judges that leak abnormality exists
when an increment of the tank internal pressure is greater than a
judgment value.
[0007] However, because the increase of the tank internal pressure
occurs owing to various factors, an erroneous judgment is likely to
be made when leak judgment is made on the basis of the comparison
result of the increment of the tank internal pressure with the
judgment value. One of the causes of the increase of the tank
internal pressure is that external air flows into the tank through
a small hole formed in the fuel tank. On the other hand, even when
no leak occurs in the fuel tank, the tank internal pressure rises
due to evaporation/dissipation of the fuel when the degree of
evaporation saturation of the fuel inside the tank is low. The fuel
is returned from the internal combustion engine into the fuel tank
through a low-pressure fuel passage. This return fuel is also a
cause of the increase of the evaporation dissipation amount.
Particularly, when the fuel remaining amount becomes small inside
the tank, evaporation/dissipation of the fuel due to this return
fuel becomes remarkable inside the tank. A winter fuel is used at
cold places from fall to spring. Because the winter fuel has a
larger content of alcohol, that is, a larger
evaporation/dissipation amount, fuel evaporation/dissipation is
remarkable particularly on warm days. The causes of the increase of
the internal pressure of the fuel tanks as criteria of the fault
diagnosis can thus be divided into the leak hole and fuel
evaporation/dissipation. In order to make a correct fault
diagnosis, it is therefore necessary to correctly judge the causes
of the increase of the tank internal pressure.
[0008] Therefore, fault judgment is tentatively made when the
increment of the tank internal pressure, measured under the closed
condition after the fault diagnosis object region, is brought into
a reduced pressure state exceeds a first judgment value, then the
increment of the tank interval pressure is measured while the fault
diagnosis object region is released to the atmosphere and then
closed, and final judgment is then made by comparing this
measurement value with a second judgment value. In other words,
when the increment of the tank internal pressure after the release
to the atmosphere is smaller than the second judgment value, final
judgment is made to the effect that a leak hole exists. When the
increment of the tank internal pressure is greater than the second
judgment value, on the other hand, the tank internal pressure is
judged as increasing due to evaporation/dissipation of the fuel. In
this case, the tentative fault judgment is withdrawn and final
judgment is made to the effect that existence/absence of the leak
hole is not known (diagnosis result by high evaporation/dissipation
judgment is invalidated).
[0009] Demands have increased in recent years to prevent
ultra-trace amount leak in the fuel evaporation/dissipation
prevention system. Ultra-small leak holes as the main cause of this
ultra-trace amount leak have diameters of about 0.5 mm. On the
other hand, the small leak holes that have so far been the object
of detection have diameters of about 1.0 mm, and the diameters of
both holes are remarkably different. When the leak holes having
different diameters are the objects of detection in fault diagnosis
of the fuel evaporation/dissipation prevention system, it becomes
more difficult to correctly discriminate whether the increment of
the tank internal pressure results from the leak holes or from
evaporation/dissipation of the fuel. In other words, the smaller
the diameter of the hole, the smaller becomes the increment of the
tank internal pressure resulting from the leak hole. To
discriminate the increase of the tank internal pressure resulting
from the ultra-small leak hole from the increase of the tank
internal pressure resulting from evaporation/dissipation of the
fuel, the second judgment value must be lowered. When the second
judgment value is set to a smaller value, however, the increment of
the tank internal pressure under the closed state after the release
to the atmosphere is likely to exceed the second judgment value.
Therefore, even when the small leak hole exists and is tentatively
judged as existing, the number of cases where the increment of the
tank internal pressure under the closed state after the release to
the atmosphere exceeds the second judgment value and leak judgment
is withdrawn becomes greater, and trace amount leak resulting from
the small leak hole cannot be detected.
[0010] It is an object of the present invention to provide a fault
diagnosis apparatus capable of accurately judging abnormality
resulting from trace amount leak and ultra-trace amount leak in the
evaporated fuel dissipation prevention system.
SUMMARY OF THE INVENTION
[0011] In the fault diagnosis apparatus according to the invention,
when a first restoring pressure amount measured after a fault
diagnosis object region of the fuel evaporation/dissipation
prevention system is brought into a reduced pressure state exceeds
a first judgment value or a second judgment value greater than the
first judgment value, a second restoring pressure amount is
measured by sealing the fault diagnosis object region after an
atmospheric pressure is introduced into the fault diagnosis object
region, the second restoring pressure amount is compared next with
a third judgment value when the first restoring pressure amount is
greater than the first judgment value but is smaller than the
second judgment value, and the second restoring pressure amount is
compared with a fourth judgment value greater than the third
judgment value when the first restoring pressure amount is greater
than the second judgment value. When the first restoring pressure
amount is greater than the first judgment value and the second
restoring pressure amount is smaller than the third judgment value,
or when the first restoring pressure amount is greater than the
second judgment value and the second restoring pressure amount is
smaller than the fourth judgment value, the fuel
evaporation/dissipation prevention system is judged as being
abnormal.
[0012] The increment of the first restoring pressure amount
resulting from the leak hole changes with a leak hole diameter.
Therefore, it is difficult to judge existence/absence of the leak
holes having various diameters without being affected by
evaporation/dissipation of the fuel. The fault diagnosis apparatus
according to claim 1 can set, respectively, the first and second
judgment values in association with ultra-trace amount leak and
trace amount leak (for example, ultra-small leak hole and small
hole respectively inducing ultra-trace amount leak and trace amount
leak) and can also set the third and fourth judgment values so that
abnormality resulting from ultra-trace amount leak and trace amount
leak can be distinguished from abnormality resulting from
evaporation/dissipation of the fuel. Therefore, ultra-trace amount
leak and trace amount leak can be distinguished from the increase
of the restoring pressure amount resulting from the fuel
evaporation/dissipation and can be correctly judged on the basis of
the restoring pressure amount.
[0013] In other words, when the first restoring pressure amount
exceeds the first judgment value as the judgment criterion of
ultra-trace amount leak but is smaller than the second judgment
value as the judgment criterion of trace amount leak, abnormality
resulting from ultra-trace amount leak is judged tentatively. Next,
the second restoring pressure amount is measured in order to
discriminate whether such an increase of the first restoring
pressure amount results from ultra-trace amount leak or from
evaporation/dissipation of the fuel. When the second restoring
pressure amount exceeds the third judgment value,
evaporation/dissipation of the fuel is judged as being the cause of
the increase of the first restoring pressure amount. In
consequence, tentative judgment of ultra-trace amount leak
abnormality is withdrawn, and final judgment is made to the effect
that existence/absence of ultra-trace amount leak is not known
(diagnosis result by high evaporation/dissipation judgment is
invalidated). When the second restoring pressure amount does not
exceed the third judgment value, on the other hand, ultra-trace
amount leak is judged as being the cause of the increase of the
first restoring pressure amount, and ultra-trace amount leak
abnormality is finally judged.
[0014] When the first restoring pressure amount exceeds the second
judgment value, abnormality resulting from trace amount leak is
judged tentatively. Next, the second restoring pressure amount is
measured to discriminate the cause of the increase of the first
restoring pressure amount. When the second restoring pressure
amount exceeds the fourth judgment value, evaporation/dissipation
of the fuel is judged as being the cause by the increase of the
first restoring pressure amount, and final judgment is made to the
effect that existence/absence of trace amount leak is not known
(diagnosis result by high evaporation/dissipation judgment is
invalidated). When the second restoring pressure amount does not
exceed the fourth judgment value, on the other hand, trace amount
leak is judged as being the cause of the increase of the first
restoring pressure amount, and trace amount leak abnormality is
finally judged as existing.
[0015] As described above, the fault diagnosis apparatus according
to the present invention can correctly judge ultra-trace amount
leak and trace amount leak, respectively, resulting from the
ultra-small leak hole and the small leak hole.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The present invention will become more fully understood from
the detailed description given hereinbelow and the accompanying
drawings which are given by way of illustration only, and thus are
not limitative of the present invention, and wherein:
[0017] FIG. 1 is a schematic view of a fuel evaporation/dissipation
prevention system equipped with a fault diagnosis apparatus
according to a first embodiment of the present invention;
[0018] FIG. 2 is a flowchart showing a part of a fault diagnosis
routine executed by an ECU shown in FIG. 1;
[0019] FIG. 3 is a flowchart showing the remaining part of the
fault diagnosis routine continuing FIG. 2;
[0020] FIG. 4 is a graph showing a change of an internal pressure
of a fuel tank with the passage of time during fault diagnosis;
[0021] FIG. 5 is a graph showing accuracy of fault diagnosis by the
fault diagnosis apparatus of the invention when the remaining
amount of the fuel is large;
[0022] FIG. 6 is a graph showing accuracy of fault diagnosis by the
fault diagnosis apparatus of the invention when the remaining
amount of the fuel is small;
[0023] FIG. 7 is a flowchart showing a fault diagnosis routine
executed by a fault diagnosis apparatus according to a second
embodiment of the present invention;
[0024] FIG. 8 is a schematic view showing a fuel
evaporation/dissipation prevention system equipped with a fault
diagnosis apparatus according to a third embodiment of the present
invention;
[0025] FIG. 9 is a flowchart showing a fault diagnosis routine
executed by the fault diagnosis apparatus according to the third
embodiment of the present invention;
[0026] FIG. 10 is a flowchart showing the remaining part of the
fault diagnosis routine continuing FIG. 9;
[0027] FIG. 11 is a graph showing a change of an internal pressure
of a fuel tank with the passage of time during fault diagnosis;
[0028] FIG. 12 is a graph showing the relation of a high
evaporation/dissipation judgment value L used in the fault
diagnosis routine shown in FIGS. 9 and 10 and an atmospheric
pressure decrement amount .DELTA.BP during measurement of a first
restoring pressure amount .DELTA.P;
[0029] FIG. 13 is a graph showing the relation between a correction
coefficient KL used for setting the high evaporation/dissipation
judgment value L in the fault diagnosis routine in a modified
embodiment of the invention and the atmospheric pressure decrement
amount .DELTA.BP; and
[0030] FIG. 14 is a flowchart for setting the high
evaporation/dissipation judgment value L in accordance with the
decrement amount of the atmospheric pressure in the fault diagnosis
routine in the modified embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] First Embodiment
[0032] A fault diagnosis apparatus according to the present
invention will be hereinafter explained with reference to the
accompanying drawings.
[0033] As shown in FIG. 1, in a fuel evaporation/dissipation
prevention system equipped with a fault diagnosis apparatus, a
canister 3 adsorbs an evaporated/dissipated fuel inside a fuel tank
1 through a vapor passage 2. When a predetermined purge condition
is established, a purge valve 7 arranged in a purge passage 4 is
opened under control of an ECU 11 to emit the evaporated/dissipated
fuel adsorbed to the canister 3 into an intake passage 6 of an
internal combustion engine 5 through the purge passage 4 and to
thus prevent emission of the evaporated/dissipated fuel into the
atmosphere.
[0034] The fault diagnosis apparatus according to the first
embodiment of the present invention diagnoses existence/absence of
leak abnormality in the fuel evaporation/dissipation prevention
system. The fault diagnosis apparatus includes a vent valve 8
fitted to the canister 3, a pressure sensor 10 for detecting the
tank internal pressure, fitted to the fuel tank 1, and the ECU 11
for controlling opening/closing of the purge valve 7 and the vent
valve 8.
[0035] In the fuel evaporation/dissipation prevention system
equipped with the fault diagnosis apparatus, when the purge valve 7
is opened while the vent valve 8 is closed, the fuel tank 1
communicates with the intake passage 6 through the vapor passage 2
and through the purge passage 4. Therefore, the fuel tank 1 is
brought into a reduced pressure state by the operation of the
negative pressure inside the intake passage 6. When the purge valve
7 is closed and the vent valve 8 is opened, on the other hand,
evaporation/dissipation of the fuel inside the fuel tank 1 elevates
the internal pressure of the fuel tank 1 to about the atmospheric
pressure.
[0036] The ECU 11 of the fault diagnosis apparatus executes the
fault diagnosis routine shown in FIGS. 2 and 3 when an ignition key
of an automobile is turned ON and a cold start of the engine is
conducted, for example.
[0037] In Step S1 of this fault diagnosis routine, the ECU 11
judges whether or not a fault diagnosis condition is established,
that is, whether or not a start cooling water temperature and an
intake temperature are below predetermined temperatures and whether
or not a fuel temperature is below a predetermined temperature, a
fuel remaining amount is within a predetermined range, and so
forth.
[0038] When the fault diagnosis condition is not judged as being
established in Step S1, the fault diagnosis in this cycle is
finished. When the fault diagnosis condition is judged as
established in Step S1, on the other hand, a tank internal pressure
increment amount represented by symbol .DELTA.P1 in FIG. 4 is
measured (Step S2). To measure this .DELTA.P1, the purge valve 7 is
closed while the vent valve 8 is opened so that the fault diagnosis
object region of the fuel evaporation/dissipation system can be
released to the atmosphere. In this instance, the purge valve 7 may
be gradually closed. The output of the pressure sensor 11
representing the tank internal pressure P1 under this
atmosphere-released state is read. When the vent valve 8 is closed
after the tank internal pressure P1 is measured, the tank internal
pressure rises with the passage of time as shown in FIG. 4.
[0039] The output of the pressure sensor 11 is read when a
predetermined time T1 passes from the measurement point of the tank
internal pressure P1, and a tank internal pressure P2 is measured
at this point. Next, a tank internal pressure increment amount
.DELTA.P1 is calculated from the tank internal pressures P1 and P2,
and measurement of .DELTA.P1 in Step S2 is finished.
[0040] In the next Step S3, whether or not the tank internal
pressure increment amount .DELTA.P1 obtained in step 2 is smaller
than a high evaporation/dissipation judgment value L1 is judged.
When the judgment result proves NO, judgment is made to the effect
that correct fault diagnosis is not possible because of an excess
fuel evaporation/dissipation, and the fault diagnosis is
finished.
[0041] On the other hand, when the tank internal pressure increment
amount .DELTA.P1 is below a leak judgment value L1, fault judgment
is further conducted. The purge valve 7 is first opened to bring
the fault diagnosis object region into a reduced pressure state in
Step S4 in FIG. 2. When the pressure detected by the pressure
sensor 11 reaches a predetermined negative pressure value indicated
by symbol P3 in FIG. 4, the purge valve 7 is closed to bring the
fault diagnosis object region into a closed state. In the fault
diagnosis object region under this closed state, the tank internal
pressure increases with the passage of time due to evaporation or
leak of the fuel inside the fuel tank 1 as shown in FIG. 4. In FIG.
4, thick solid line represents leak of a trace amount and thin
solid line does leak of a ultra-trace amount. When a predetermined
time T2 passes from the point of time at which the purge valve 7 is
closed, the output of the pressure sensor 10 representing the tank
internal pressure P4 at this point of time is read, and the tank
internal pressure increment value .DELTA.P as the first restoring
pressure value is calculated from the tank internal pressures P3
and P4.
[0042] In the next Step S5, whether or not the first restoring
pressure amount .DELTA.P calculated in Step S4 is greater than a
first judgment value L11 suitable for the judgment of the
ultra-trace amount leak resulting mainly from a ultra-small leak
hole is judged. When the judgment result proves NO, leak
abnormality is not judged as existing and the fault diagnosis is
finished.
[0043] On the other hand, when the first restoring pressure amount
.DELTA.P is greater than the first judgment value L11, whether or
not the first restoring pressure amount .DELTA.P is greater than a
second judgment value L12 suitable for the judgment of trace amount
leak resulting mainly from a small leak hole is judged (Step S6).
When the judgment result of Step S6 proves YES, a value of a flag F
representing the number of times that the first restoring pressure
amount .DELTA.P exceeds the second judgment value L12 is
incremented by "1" in Step S7. The flow then proceeds to Step S8 of
FIG. 3. When the judgment result in Step S6 proves NO, on the other
hand, the flow immediately proceeds from Step S6 to Step S8, and
the number of times of measurement of the first restoring pressure
amount .DELTA.P is incremented by "1". Next, whether or not the
number of times of measurement N is equal to "3" is judged (Step
S9). When the number of times of measurement of the first restoring
pressure amount .DELTA.P does not reach 3 times, the flow proceeds
to Step S4 of FIG. 2 and the first restoring pressure amount
.DELTA.P is again measured.
[0044] When the first restoring pressure amount .DELTA.P is
measured three times in this way, the judgment result in Step S9
becomes YES, and whether or not the value of the flag F is "3" is
judged in Step S10. When the judgment result in Step S10 is NO,
that is, when all of the first restoring pressure amounts .DELTA.P
measured thrice are below the second judgment value L12, judgment
is made tentatively that ultra-trace amount leak resulting mainly
from a ultra-small leak hole exists. Next, a judgment value L used
for high evaporation/dissipation judgment to be explained next is
set to a third judgment value L21 suitable for discriminating
ultra-trace amount leak from high evaporation/dissipation (Step
S11). On the other hand, when the judgment result of Step S10 is
YES, that is, when all the first restoring pressure amounts
.DELTA.P measured thrice exceed the second judgment value L12,
judgment is tentatively made that trace amount leak resulting
mainly from a small leak hole exists, and the judgment value L is
set to a fourth judgment value L22 suitable for discriminating
trace amount leak from high evaporation/dissipation (Step S12).
[0045] In the next Step S13, the purge valve 7 is closed while the
vent valve 8 is opened so as to release the fault diagnosis object
region to the atmosphere. After the tank internal pressure P5 under
this atmosphere-released state is measured through the pressure
sensor, the vent valve 8 is closed and the fault diagnosis object
region is brought into the closed state. The tank internal pressure
increases under this closed state with the passage of time as shown
in FIG. 4. When a predetermined time T3 passes from the point of
time at which measurement of the tank internal pressure P5 is
finished, the output of the pressure sensor 10 is read, the tank
internal pressure P6 at this point of time is measured, and
re-.DELTA.P1 as the second restoring pressure amount is calculated
from the tank internal pressures P5 and P6.
[0046] In the next Step S14, whether or not this re-.DELTA.P1 is
greater than the judgment value L set in Step S11 or S12 is judged.
When the judgment result proves NO, final judgment is made in Step
S15 to the effect that leak exists. When the judgment result in
Step S14 proves YES, on the other hand, judgment is made to the
effect that because the increase of the first restoring amount
.DELTA.P results from high evaporation/dissipation, the tentative
judgment that leak exists must be withdrawn, and the fault
diagnosis is finished without making leak judgment. Incidentally,
when leak is judged as existing, the leak judgment result is
notified by use of an alarm lamp or an alarm buzzer.
[0047] In summary, in this embodiment the first and second judgment
values L11 and L12 are set in association with ultra-trace amount
leak and trace amount leak, respectively, and the third and fourth
judgment values L21 and L22 are set so that abnormality resulting
respectively from ultra-trace amount leak and from trace amount
leak can be discriminated from abnormality resulting from
evaporation/dissipation of the fuel. When the first restoring
pressure amount .DELTA.P exceeds the first judgment value L11 as
the judgment criterion of ultra-trace amount leak and is below the
second judgment value L12 as the judgment criterion of trace amount
leak, abnormality resulting from the ultra-trace amount leak is
tentatively judged. Next, the second restoring pressure amount
(re-.DELTA.P1) is measured in order to judge whether the increase
of such a first restoring pressure amount results from ultra-trace
amount leak or from excessive evaporation/dissipation of the
fuel.
[0048] When the second restoring pressure amount exceeds the third
judgment value L21, evaporation/dissipation of the fuel is judged
as the cause of the increase of the first restoring pressure
amount, and tentative judgment of ultra-trace amount leak
abnormality is withdrawn and final judgment is made to the effect
that existence/absence of ultra-trace amount leak is not known
(diagnosis by high evaporation/dissipation judgment is
invalidated). On the other hand, when the second restoring pressure
amount does not exceed the third judgment value, ultra-trace amount
leak is judged as being the cause of the increase of the first
restoring pressure amount, and ultra-trace amount leak abnormality
is judged finally.
[0049] When the first restoring pressure amount .DELTA.P exceeds
the second judgment value L12, abnormality resulting from trace
amount leak is tentatively judged. Next, the second restoring
pressure amount (re-.DELTA.P1) is measured for judging the cause of
the increase of the first restoring pressure amount. When the
second restoring pressure amount exceeds the fourth judgment value
L22, evaporation/dissipation of the fuel is judged as the cause of
the increase of the first restoring pressure amount .DELTA.P, and
final judgment is made to the effect that existence/absence of
trace amount leak is not known (diagnosis by high
evaporation/dissipation judgment is invalidated). When the second
restoring pressure amount does not exceed the fourth judgment value
L22, on the other hand, trace amount leak is judged as the cause of
the increase of the first restoring pressure amount and final
judgment is made to the effect that trace amount leak exists. It
becomes thus possible to accurately judge ultra-trace amount leak
and trace amount leak.
[0050] Additionally, the ECU 11 of the fault diagnosis apparatus
operates as first diagnosis means for comparing the first restoring
pressure amount .DELTA.P measured after pressure reduction of the
fault diagnosis object region with the first judgment value L11 or
the second judgment value L12, as second diagnosis means for
comparing the second restoring pressure value (re-.DELTA.P1)
measured under the closed state after the fault diagnosis object
region is released to the atmosphere with the third judgment value
L21 or the fourth judgment value L22, and as abnormality judgment
means for judging abnormality of the fuel evaporation/dissipation
prevention system on the basis of the first and second restoring
pressure amounts.
[0051] The inventors of the present invention have produced the
fuel evaporation/dissipation prevention system equipped with the
fault diagnosis apparatus as set forth in the embodiment described
above, have set the first to fourth judgment values L11, L12, L21,
and L22, and have evaluated fault diagnosis accuracy. FIG. 5 shows
the fault diagnosis result when the fuel remaining amount inside
the fuel tank 1 is from 40 to 85%. FIG. 6 shows the fault diagnosis
result when the fuel remaining amount is from 15 to 40%. In FIGS. 5
and 6, "o" mark represents the diagnosis result of a fuel
evaporation/dissipation prevention system without leak, "*" mark
represents the diagnosis result of a fuel evaporation/dissipation
prevention system provided with a ultra-small leak hole having a
0.5 mm diameter that causes ultra-trace amount leak, and ".DELTA."
mark represents the diagnosis result of a fuel
evaporation/dissipation prevention system provided with a small
leak hole having a 1.0 mm diameter that causes trace amount
leak.
[0052] It can be understood from FIG. 5 that, in the fuel
evaporation/dissipation system without leak, the first restoring
pressure value .DELTA.P is in many cases below the first judgment
value L11 and normal judgment is correctly made in most cases as
represented by the "o" mark. When the first restoring pressure
amount exceeds the first judgment value, the re-.DELTA.P1 exceeds
the third judgment value L21 or the fourth judgment value L22 and
judgment is made as high evaporation/dissipation judgment. In other
words, a correlation exists between the first restoring pressure
amount .DELTA.P and re-.DELTA.P1. Since re-.DELTA.P1 increases with
the increase of the first restoring pressure amount .DELTA.P, leak
judgment is not made. As to the case represented by an oval region
in FIG. 5, normal judgment can be made by variably setting the
first judgment value L11 in accordance with the fuel temperature
and the fuel remaining amount.
[0053] In the system having the ultra-small leak hole, leak
judgment is made correctly in almost all the cases as represented
by the ".circle-solid." mark, but high evaporation/dissipation
judgment is sometimes made when evaporation/dissipation of the fuel
is great. In the system having the small leak hole, leak judgment
is correctly made in almost all the cases as represented by the
.DELTA. mark. It can be understood that when the first restoring
pressure amount .DELTA.P exceeds the second judgment value L12 as
in the case of a circle region in FIG. 5, in particular, leak
judgment can be correctly made by use of the fourth judgment value
L22 greater than the third judgment value L21 as the judgment
criterion value of the second restoring pressure value
(re-.DELTA.P1).
[0054] As is apparent from FIG. 6, fault diagnosis accuracy
analogous to that of FIG. 5 can be obtained also when the fuel
remaining amount is small. As represented by the circle region in
FIG. 6, in particular, the effect of using the fourth judgment
value L22 appears remarkably. It has thus been confirmed that the
fault diagnosis apparatus can be suitably used for fault diagnosis
in the low fuel amount region. However, ultra-small leak is judged
in some cases as high evaporation/dissipation as represented by the
elliptic region in FIG. 6.
[0055] Second Embodiment
[0056] A fault diagnosis apparatus according to the second
embodiment of the present will be explained.
[0057] The fault diagnosis apparatus according to this embodiment
basically has the same construction as that of the first
embodiment. In the fuel evaporation/dissipation prevention system
according to the first embodiment, the first restoring pressure
amount .DELTA.P, measured under the closed state after pressure
reduction of the fault diagnosis object region of the fuel
evaporation/dissipation prevention system, is serially compared
with the first and second judgment values L11 and L12, and the
second restoring pressure amount (re-.DELTA.P1), measured under the
closed state after the fault diagnosis object region is released to
the atmosphere, is compared with the third judgment value L21 or
the fourth judgment value L22. In contrast, in this embodiment, the
first restoring pressure value .DELTA.P is compared with a first
predetermined value L3, and a second predetermined value L4 to be
compared with the second restoring pressure amount is set in
accordance with the first restoring pressure amount .DELTA.P.
[0058] More concretely, the ECU 11 of the fault diagnosis apparatus
of this embodiment periodically executes the fault diagnosis
routine shown in FIG. 7. In this fault diagnosis routine, Steps S1
to S5A corresponding respectively to Steps S1 to S5 in FIG. 2 are
executed. In Step S5A, the first restoring pressure amount
.DELTA.P1 is compared with the first predetermined value L3 in
place of the first judgment value L11 in Step S5 in FIG. 2. When
the judgment result of Step 5A is YES, steps similar to Steps S8
and S9 in FIG. 3 are serially executed.
[0059] When the judgment result in Step S9 proves YES, that is,
when all the first restoring pressure amounts .DELTA.P1 measured
thrice exceed the first predetermined value L3, the second
predetermined value L4 is set in accordance with the first
restoring pressure amount .DELTA.P (the maximum value, the minimum
value or the mean value of the first restoring pressure amounts
.DELTA.P measured thrice). More concretely, the second
predetermined value L4 is set to a greater value when the first
restoring pressure amount .DELTA.P is greater (Step S11A). Next,
Steps S13, S14A, and S15 respectively corresponding to Steps S13 to
S15 in FIG. 3 are serially executed. In Step S14A, whether or not
re-.DELTA.P1 is greater than the second predetermined value L4 is
judged.
[0060] The ECU 11 of the fault diagnosis apparatus operates as
first diagnosis means for comparing the first restoring pressure
amount .DELTA.P measured after pressure reduction of the fault
diagnosis object region of the fuel evaporation/dissipation
prevention system with the first predetermined value L3, as second
diagnosis means for comparing the second restoring pressure amount
(re-.DELTA.P1) measured under the closed state after the fault
diagnosis object region is released to the atmosphere with the
second predetermined value L4 and as abnormality judgment means for
judging abnormality of the fuel evaporation/dissipation prevention
system on the basis of the first and second restoring pressure
amounts.
[0061] In the second embodiment, when the first restoring pressure
amount .DELTA.P exceeds the first predetermined value L3 as the
judgment criterion of ultra-trace amount leak or trace amount leak,
leak abnormality is tentatively judged. Next, the second restoring
pressure amount (re-.DELTA.P1) is measured for judging the cause of
the increase of the first restoring pressure amount .DELTA.P, and
the second restoring pressure amount is compared with the second
predetermined value L4. The second predetermined value L4 is set in
accordance with the first restoring pressure amount .DELTA.P and is
adaptive to ultra-trace amount leak or trace amount leak. When the
second restoring pressure amount exceeds the second predetermined
value (third judgment value and fourth judgment value) L4, judgment
is made that the increase of the first restoring pressure amount
.DELTA.P results from the excessive evaporation/dissipation of the
fuel and tentative judgment of leak abnormality is withdrawn. When
the second restoring pressure amount does not exceed the second
predetermined value L4, on the other hand, judgment is made to the
effect that the increase of the first restoring pressure amount
.DELTA.P results from leak abnormality, and leak abnormality is
judged finally. As described above, the fault diagnosis apparatus
according to this embodiment accurately discriminates ultra-trace
amount leak from trace amount leak while preventing erroneous
judgment resulting from evaporation/dissipation of the fuel.
[0062] The invention is not limited to the first and second
embodiments given above, but can be changed or modified in various
ways. For example, the features of the first and second embodiments
maybe combined with one another. More concretely, the judgment
value L may be set in accordance with the first restoring pressure
amount .DELTA.P in Steps S11 and S12 in FIG. 3. The invention can
be changed or modified in various other ways within the scope of
the invention.
[0063] Third Embodiment
[0064] A fault diagnosis apparatus according to a third embodiment
of the present invention will be hereinafter explained.
[0065] The fault diagnosis apparatus of this embodiment is
different from the first embodiment in that it is equipped with an
atmospheric pressure sensor 12 as shown in FIG. 8 but is basically
has the same construction. Therefore, detailed explanation will be
omitted.
[0066] The fault diagnosis apparatus according to the third
embodiment is employed for diagnosing existence/absence of leak
abnormality in the fuel evaporation/dissipation system and includes
a vent valve 8 fitted to a canister 3, a pressure sensor 10 for
detecting a tank internal pressure, fitted to a fuel tank 1, an ECU
11 for controlling opening/closing of a purge valve 7 and the vent
valve 8 and an atmospheric pressure sensor 12 connected to the
input side of the ECU 11. The pressure sensor 10 comprises a
relative pressure sensor for detecting a relative pressure inside
and outside the fuel tank 1 as the fuel tank internal pressure.
When the atmospheric pressure decreases with driving of the
automobile having the apparatus of the present invention mounted
thereto on a slope, the fuel tank internal pressure detected by the
pressure sensor 10 increases by a decrement of the atmospheric
pressure.
[0067] When the purge valve 7 is opened while the vent valve 8 is
closed in the fuel evaporation/dissipation prevention system
equipped with the fault diagnosis apparatus, the fuel tank 1
communicates with an intake passage 6 through a vapor passage 2 and
a purge passage 2. In consequence, the internal pressure of the
fuel tank 1 is reduced due to the operation of a negative pressure
inside the intake passage 6. When the purge valve 7 is closed while
the vent valve 8 is opened, on the other hand, the internal
pressure of the fuel tank 1 increases to about the atmospheric
pressure. When both of the purge valve 7 and the vent valve 8 are
thereafter closed, the internal pressure of the fuel tank 1
increase above the atmospheric pressure due to evaporation and
dissipation of the fuel inside the fuel tank 1.
[0068] The ECU 11 of the fault diagnosis apparatus executes a fault
diagnosis routine shown in FIGS. 9 and 10 at the time of cold start
when an ignition key of the automobile is turned on, for
example.
[0069] In Step S101 of the fault diagnosis routine, the ECU 11
judges whether or not a fault diagnosis condition is established,
that is, whether or not a start cooling water temperature and an
intake temperature are below predetermined temperatures and whether
or not a fuel temperature is below a predetermined temperature, a
fuel remaining amount is within a predetermined range, and so
forth.
[0070] When the fault diagnosis condition is not judged as being
established in Step S101, the fault diagnosis in this cycle is
finished When the fault diagnosis condition is judged as
established in Step S101, on the other hand, a tank internal
pressure increment amount represented by symbol .DELTA.P1 in FIG.
11 is measured (Step S102). To measure this .DELTA.P1, the purge
valve 7 is closed while the vent valve 8 is opened so that the
fault diagnosis object region of the fuel evaporation/dissipation
prevention system can be released to the atmosphere. In this case,
the purge valve 7 may be gradually closed. The output of the
pressure sensor 10 representing the tank internal pressure P1 under
this atmosphere-released state is read. When the vent valve 8 is
closed after the tank internal pressure P1 is measured, the tank
internal pressure rises with the passage of time as shown in FIG.
11.
[0071] The output of the pressure sensor 10 is read when a
predetermined time T1 passes from the measurement point of the tank
internal pressure P1, and a tank internal pressure P2 is measured
at this point. Next, a tank internal pressure increment amount
.DELTA.P1 is calculated from the tank internal pressures P1 and P2,
and measurement of .DELTA.P1 in Step S102 is finished.
[0072] In the next Step S103, whether or not the tank internal
pressure increment amount .DELTA.P1 is smaller than a high
evaporation/dissipation judgment value L1. When the judgment result
proves NO, judgment is made to the effect that correct fault
diagnosis is not possible because of the excess of the fuel
evaporation/dissipation (Step S103a) and then fault diagnosis is
finished.
[0073] On the other hand, when the tank internal pressure increment
amount .DELTA.P1 is below a leakage judgment value L1, fault
judgment is further conducted. The purge valve 7 is first opened to
bring the fault diagnosis object region into a reduced pressure in
Step S104 in FIG. 9. When the pressure detected by the pressure
sensor 10 reaches a predetermined negative pressure value indicated
by symbol P3 in FIG. 11, the purge valve 7 is closed to bring the
fault diagnosis object region into a closed state. In the fault
diagnosis object region under this closed state, the tank internal
pressure increases with the passage of time due to evaporation or
leak of the fuel inside the fuel tank 1 as shown in FIG. 11. When a
predetermined time T2 passes from the point of time at which the
purge valve 7 is closed, the output of the pressure sensor 10
representing the tank internal pressure P4 at this point of time is
read, and the tank internal pressure increment amount .DELTA.P as
the first restoring pressure amount is calculated from the tank
internal pressures P3 and P4.
[0074] In the next Step S105, whether or not the first restoring
pressure amount .DELTA.P calculated in Step S104 is greater than a
first judgment value L11 suitable for the judgment of ultra-trace
amount leak resulting mainly from a ultra-small leak hole is
judged. When the judgment result proves NO, leak abnormality is not
judged as existing (Step S105a) and the fault diagnosis is
finished.
[0075] On the other hand, when the first restoring pressure amount
.DELTA.P is greater than the first judgment value L11, whether or
not the first restoring pressure amount .DELTA.P is greater than a
second judgment value L12 suitable for the judgment of trace amount
leak resulting mainly from a small leak hole is judged (Step S106).
When the judgment result of Step S106 proves YES, a value of a flag
F representing the number of times that the first restoring
pressure amount .DELTA.P exceeds the second judgment value L12 is
incremented by "1" (in Step S107). The flow then proceeds to Step
S108. When the judgment result in Step S106 proves NO, that is,
when the first restoring pressure amount .DELTA.P is smaller than
the second judgment value L12, on the other hand, the flow
immediately proceeds from Step S6 to Step S108.
[0076] In Step S108, whether or not a flag Fbp has a value "1"
representing that a decrement amount .DELTA.BP of the atmospheric
pressure BP during the measurement of the first restoring pressure
amount .DELTA.P is greater than a predetermined amount Bpa is
judged. When the judgment result in this Step S108 is YES (flag
Fbp=1), the control flow proceeds to Step S112 in FIG. 10.
[0077] On the other hand, when the judgment result in Step S108 is
NO (Fbp.noteq.1), that is, when the atmospheric pressure is judged
not having decreased until the previous measurement of .DELTA.P
till, whether or not the decrease of the atmospheric pressure
occurs during the measurement of .DELTA.P made this time is judged.
Therefore, the atmospheric pressure BP1 that is detected by the
atmospheric pressure sensor 12 when the tank internal pressure
reaches a predetermined negative pressure P3 and is temporarily
stored in a memory and an atmospheric pressure BP2 that is detected
when a predetermined time T2 passes from the arrival at the
predetermined negative pressure P3 and is temporarily stored are
read out from the memory, and BP2 is subtracted from BP1 to
determine the atmospheric pressure decrement amount .DELTA.BP.
Furthermore, whether or not this change amount .DELTA.BP is greater
than a predetermined amount BPa is judged (Step S109). When the
decrement of the atmospheric pressure greater than the
predetermined amount BPa is judged as existing during measurement
of the first restoring pressure amount .DELTA.P, a value "1" is set
to the flag Fbp (Step S110). When such a decrement of the
atmospheric pressure is not judged as existing, a value "0" is set
to the flag Fbp (Step S111).
[0078] In Step S112 following Step S108, S110 or Step S112, the
number of times of measurement of the first restoring pressure
amount .DELTA.P is incremented by "1". Next, whether or not the
number of times of measurement N is equal to "3" is judged (Step
S113). When the number of times of measurement of the first
restoring pressure amount .DELTA.P does not reach 3, the flow
proceeds to Step S104 of FIG. 2 and the first restoring pressure
amount .DELTA.P is again measured. When the first restoring
pressure amount .DELTA.P is measured three times in this way, the
judgment result in Step S113 becomes YES, and whether or not the
value of the flag F is "3" is judged in next Step S114.
[0079] When the judgment result in Step S114 is NO, that is, when
all of the first restoring pressure amounts .DELTA.P measured
thrice are below the second judgment value L12, judgment is made
tentatively that ultra-trace amount leak resulting mainly from a
ultra-small leak hole exists. Next, a judgment value L used for
high evaporation/dissipation judgment to be explained next is set
to a third judgment value L21 suitable for discriminating
ultra-trace amount leak from high evaporation/dissipation (Step
S116).
[0080] By contrast, when all the first restoring pressure amounts
.DELTA.P measured thrice are judged to have exceeded the second
judgment value L12 in Step S114, whether or not the flag Fbp has a
value "1" is judged in next Step S115.
[0081] When the judgment result in Step S115 is NO, that is, when
the atmospheric pressure does not change more than the
predetermined value BPa during the thrice measurements of the first
restoring pressure amount .DELTA.P, judgment is made tentatively
that trace amount leak mainly resulting from a small leak hole
exists, and a high evaporation/dissipation judgment value L is set
to a fourth judgment value L22 suitable for discriminating trace
amount leak from high evaporation/dissipation (Step S117).
[0082] On the other hand, when the judgment result in Step S115 is
YES, that is, the drop of the atmospheric pressure exceeding the
predetermined value BPa is detected even once during the thrice
measurements of the first restoring pressure amount .DELTA.P, the
high evaporation/dissipation judgment value L is set to a third
judgment value 21 suitable for trace amount leak judgment and
smaller than the fourth judgment value L22 although judgment is
made in Step S114 that the first restoring pressure amount .DELTA.P
is great and the possibility of trace amount leak exists (Step
S115).
[0083] In other words, when the atmospheric pressure BP decreases
by a value greater than the predetermined pressure during the
measurement of .DELTA.P due to driving on a slope having an acute
gradient, the measurement value of the fuel tank internal pressure
by the pressure sensor 10 comprising the relative pressure sensor
increases relatively from a tank internal pressure change curve
indicated by one-dot-chain line in FIG. 11 towards a curve
indicated by solid line as indicated by white arrow. Therefore,
when high evaporation/dissipation judgment is made by use of the
judgment value L that is the same as the high
evaporation/dissipation judgment value during driving on a flat
land without involving the drop of the atmospheric pressure, the
judgment value L becomes excessive by the decrement of the
atmospheric pressure and erroneous judgment of the existence of
leak abnormality is likely to be made although leak abnormality
does not exist in practice.
[0084] In this point, when the fourth judgment value L22 is
replaced with the third judgment value L21 in Step S115, as
indicated by thick downward arrow in FIG. 11 and as also shown in
FIG. 12, at the time of the drop of the atmospheric pressure even
when the first restoring pressure amount is great, the fourth
judgment value L22 is corrected to decrease and the erroneous
judgment can be avoided.
[0085] In Step S118 of the fault diagnosis routine, the purge valve
7 is closed while the vent valve 8 is opened to release the fault
diagnosis object region to the atmosphere. After the pressure
sensor 10 measures the tank internal pressure P5 under this
released state, the vent valve 8 is closed to bring the fault
diagnosis object region into the closed state. Under this closed
state, the tank internal pressure increases with the passage of
time as shown in FIG. 11. When a predetermined time T3 passes from
the finish point of the measurement of the tank internal pressure
P5, the output of the pressure sensor 10 is read, the tank internal
pressure P6 at this point is measured, and re-.DELTA.P1 as the
second restoring pressure amount is calculated from the tank
internal pressures P5 and P6.
[0086] In the next Step S119, whether or not this re-.DELTA.P1 is
(greater than the judgment value L set in Step S116 or S117. When
the judgment result proves NO, final judgment is made in Step 120
to the effect that leak exists. When the judgment result in Step
119 proves YES, on the other hand, judgment is made to the effect
that because the increase of the first restoring amount .DELTA.P
results from high evaporation/dissipation, the tentative judgment
to the effect that leak exists must be withdrawn (Step S121), and
the fault diagnosis is finished without making the leak
judgment.
[0087] The fourth judgment value L22 used for the final judgment at
the time of the decrease of the atmospheric pressure is corrected
to decrease as described above, the possibility that leak
abnormality is erroneously judged to exist due to the excess of
this judgment value by the decrement of the atmospheric pressure
can be reduced. Incidentally, when leak is judged as existing in
Step S120, the leak judgment result is notified by use of an alarm
lamp or an alarm buzzer.
[0088] In summary, the first and second judgment values L11 and L12
in this embodiment are set in association with ultra-trace amount
leak and trace amount leak, respectively, and the third and fourth
judgment values L21 and L22 are set so that abnormality resulting
from ultra-trace amount leak and trace amount leak can be
discriminated from abnormality resulting from
evaporation/dissipation of the fuel.
[0089] When the first restoring pressure amount .DELTA.P exceeds
the first judgment value L11 as the judgment criterion of the
ultra-trace amount leak and is below the second judgment value L12
as the judgment criterion of trace amount leak, abnormality
resulting from the ultra-trace amount leak is tentatively judged.
Next, the second restoring pressure amount (re-.DELTA.P1) is
measured in order to judge whether such increase of the first
restoring pressure amount results from ultra-trace amount leak or
from excessive evaporation/dissipation of the fuel.
[0090] When the second restoring pressure amount exceeds the third
judgment value L21, evaporation/dissipation of the fuel is judged
as the cause of the increase of the first restoring pressure amount
.DELTA.P, and tentative judgment of ultra-trace amount leak
abnormality is withdrawn and final judgment is made to the effect
that existence/absence of ultra-trace amount leak is not known
(diagnosis by high evaporation/dissipation judgment is
invalidated). On the other hand, when the second restoring pressure
amount does not exceed the third judgment value, ultra-trace amount
leak is judged as being the cause of the increase of the first
restoring pressure amount, and ultra-trace amount leak abnormality
is judged finally.
[0091] When the first restoring pressure amount .DELTA.P exceeds
the second judgment value L12, abnormality resulting from trace
amount leak is tentatively judged. Next, the second restoring
pressure amount (re-.DELTA.P1) is measured for judging the cause of
the increase of the first restoring pressure amount. When the
second restoring pressure amount exceeds the fourth judgment value
L22, evaporation/dissipation of the fuel is judged as the cause of
the increase of the first restoring pressure amount .DELTA.P, and
final judgment is made to the effect that existence/absence of
trace amount leak is not known (diagnosis by high
evaporation/dissipation judgment is invalidated). When the second
restoring pressure amount does not exceed the fourth judgment value
L22, on the other hand, trace amount leak is judged as the cause of
the increase of the first restoring pressure amount and final
judgment is made to the effect that trace amount leak exists. It
becomes thus possible to accurately judge ultra-trace amount leak
and trace amount leak.
[0092] Since this embodiment uses the pressure sensor 10 for
detecting the relative pressure inside and outside the fuel tank to
measure the fuel tank internal pressures P1 to P6, there is a
possibility that the measurement value relatively increases by the
decrement of the atmospheric pressure when the atmospheric pressure
drops during the measurement of the tank internal pressure, so that
leak judgment is likely to be erroneous. However, when the
atmospheric pressure drops more than the predetermined amount BPa
during measurement of .DELTA.P, the fourth judgment value L22 to be
compared with the second restoring pressure amount (re-.DELTA.P1)
in the subsequent high evaporation/dissipation judgment is
corrected so as to decrease. Therefore, this embodiment can
correctly judge existence/absence of trace amount leak abnormality
without affected by the change of the atmospheric pressure. Because
the decrement correction of the fourth judgment value L22 is made
by replacing the fourth judgment value L22 by the third judgment
value L21, the construction relating to the leak judgment and the
judgment procedure become simple.
[0093] Additionally, the ECU 11 of the fault diagnosis apparatus
operates as first diagnosis means for comparing the first restoring
pressure amount .DELTA.P measured after pressure reduction of the
fault diagnosis object region with the first judgment value L11 or
the second judgment value L12, as second diagnosis means for
comparing the second restoring pressure value (re-.DELTA.P1)
measured under the closed state after the fault diagnosis object
region is released to the atmosphere with the third judgment value
L21 or the fourth judgment value L22, as abnormality judgment means
for judging abnormality of the fuel evaporation/dissipation
prevention system on the basis of the first and second restoring
pressure amounts, and as correction means for correcting and
decreasing the fourth judgment value L22 when the atmospheric
pressure drops.
[0094] The present invention is not limited to the third embodiment
described above, but can be changed or modified in various
ways.
[0095] For example, in the embodiment described above, the fourth
judgment value L22 is so corrected as to decrease when the drop of
the atmospheric pressure beyond the predetermined amount BPa is
detected at least once during the thrice measurements of .DELTA.P.
However, this decreasing correction may be conducted when the drop
of the atmospheric pressure is detected a plurality of times or
when the maximum value, the minimum value or the mean value of the
drop of the atmospheric pressure exceeds the predetermined amount
BPa during the thrice measurement of .DELTA.P. Incidentally,
.DELTA.P measurement is not limited to three times.
[0096] It is not essentially necessary to correct and decrease
step-wise the high evaporation/dissipation judgment value L from
L22 to L21 as shown in FIG. 12 when the atmospheric pressure
decrement amount .DELTA.BP is greater than the predetermined value
BPa. The judgment value L may be corrected and decreased by
multiplying the judgment value L by a correction coefficient KL,
that decreases from a value 1 when the atmospheric pressure
decrement amount .DELTA.BP increases, as shown in FIG. 13.
[0097] In the embodiment described above, only the fourth judgment
value L22 is corrected and decreased when the atmospheric pressure
drops. However, both of the third and fourth judgment values L21
and L22 may be corrected. In this case, it is possible to correct
step-wise each judgment value corresponding to the predetermined
amount BPa or to correct it step-wise corresponding to a plurality
of predetermined amounts as shown in FIG. 12, or to correct it so
as to gradually decrease as shown in FIG. 13.
[0098] In the embodiment described above, the third and fourth
judgment values L21 and L22 remain constant irrespective of the
first restoring pressure amount .DELTA.BP. However, it is also
possible to variably set both judgment values L21 and L22 in
accordance with the first restoring pressure amount .DELTA.P or to
variably set one of both judgment values that is to be compared
with the second restoring pressure amount (re-.DELTA.P1) in
accordance with .DELTA.P. Also in this modified embodiment, when
the drop of the atmospheric pressure exceeding the predetermined
pressure occurs during .DELTA.P measurement either one, or both, of
the third and fourth judgment values L21 and L22 may be corrected
to decrease. This correction is preferably made in accordance with
the decreasing amount of the atmospheric pressure.
[0099] In this case, the third judgment value L21 or the fourth
judgment value L22 maybe set in accordance with the decreasing
amount of the atmospheric pressure in Steps S201 to S205 in FIG. 14
in place of Steps S114 to 117 in FIG. 10 in the third
embodiment.
[0100] In Step S201 in FIG. 14, whether or not the value of the
flag F is "3" is judged.
[0101] When the judgment result of Step S201 proves NO, that is,
when any of the first restoring pressure amount .DELTA.P measured
three times is judged below the second judgment value L12, judgment
is made tentatively to the effect that ultra-trace leak resulting
mainly from the ultra-small leak hole exists. In Step S202, whether
or not the flag Fbp has a value "1" representing that the decrement
amount .DELTA.BP of the atmospheric pressure BP during measurement
of the first restoring pressure amount .DELTA.P is greater than the
predetermined amount BPa is judged. When the judgment result in
this Step S108 proves YES (flag Fbp=1), the flow proceeds to Step
S203 and the third judgment value L21 is set in accordance with the
decrement amount of the atmospheric pressure. On the other hand,
when this judgment result proves NO, the judgment value L used for
the high evaporation/dissipation judgment in Step 204 is set to the
third judgment value L21 suitable for discriminating the
ultra-trace amount leak from high evaporation/dissipation.
[0102] By contrast, when Step S201 judges that all the first
restoring pressure amounts .DELTA.P measured thrice exceed the
second judgment value L12 in Step S201, judgment is made
tentatively to the effect that trace amount leak resulting mainly
from the small leak hole exists, and whether or not the flag Fbp
has the value "1" is judged in the next Step S205.
[0103] In Step S205, whether or not the flag Fbp has the value "1"
representing that the decrement amount .DELTA.BP of the atmospheric
pressure BP during measurement of the first restoring pressure
amount .DELTA.P exceeds the predetermined amount BPa is judged.
When the judgment result in this Step S108 proved YES (flag Fbp=1),
the flow proceeds to Step S206 and the fourth judgment value L22 is
set in accordance with the decrement amount of the atmospheric
pressure. When the judgment result proves NO, on the other hand,
the judgment value L used for high evaporation/dissipation judgment
in Step S207 is set to the fourth judgment value L22 suitable for
discriminating trace amount leak from high
evaporation/dissipation.
[0104] The invention can be changed or modified in various other
ways within the scope thereof.
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